The Order of Time

by Carlo Rovelli

Time has lost its first aspect or layer: its unity. It has a different rhythm in every different place and passes here differently from there. The things of this world interweave dances made to different rhythms. If the world is upheld by the dancing Shiva, there must be ten thousand such dancing Shivas, like the dancing figures painted by Matisse.

austere Prussian professor called Rudolf Clausius. It is he who grasps the fundamental issue at stake, formulating a law that was destined to become famous: If nothing else around it changes, heat cannot pass from a cold body to a hot one.

This is the only basic law of physics that distinguishes the past from the future.

Heat is the microscopic agitation of molecules. Hot tea is tea in which the molecules are very agitated. Cold tea is tea in which the molecules are only a little agitated.

Time has lost another of its crucial components: the intrinsic difference between past and future.

If your sister is on Proxima b, however, light takes four years to reach you from there. Hence, if you look at her through a telescope, or receive a radio communication from her, you know what she was doing four years ago rather than what she is doing now.

Our “present” does not extend throughout the universe. It is like a bubble around us.